1. Field of the Invention
The present invention relates to a linear oscillatory actuator, and more particularly to a single-winding linear oscillatory actuator realizing a linear reciprocal movement of a mover at a large force in one direction and at a small force in the other direction.
2. Description of Background Art
It has been conventionally used a linear oscillatory actuator using a magnetic force in many mechanical instruments required to be driven in the linear reciprocal movement. It is known such a linear oscillatory actuator includes the moving coil type, moving iron-core type, and moving magnet type.
One of representative structures of the single-winding linear oscillatory actuator is that of the moving iron-core type combined with a spring for a mechanical operation (herein after referred to a “first example”).
More particularly, the first example includes a single-winding excitation coil mounted on a stator core having substantially a “C”-shaped configuration. This structure also includes a spring for biasing in a predetermined direction. The spring is mounted on a mover of magnetic material arranged within the stator core. With this configuration a reciprocal movement can be achieved. The mover is attracted by a magnetic flux generated when a current is supplied to the excitation coil. The mover is returned to its initial position by the restoring force of the spring when the supply of the current to the excitation coil is stopped.
Another example of structure of a single-winding linear oscillatory actuator is disclosed in the article “The development of a single-winding linear oscillatory actuator and the high power design thereof”(The Transactions of The Institute of Electrical Engineers of Japan D, 1993, vol. 113-D, No. 1, pp. 120˜125) (herein after referred to a “second example”).
The second example is classified as a moving magnet type in which a single-winding excitation coil is mounted on a stator core having substantially a “C”-shaped configuration and a permanent axially magnetized magnet is sandwiched by salient poles. The mover is moved in a predetermined direction by the generation of alternately an attractive force and a repulsive force between the magnetic poles of the stator core and those of the mover. These forces are generated by supplying a current to the excitation coil. By reversing the direction of the current supplied to the excitation coil, the mover is moved in reverse direction due to the accompanying change in the magnetic pole generated in the stator core, and, thus, the mover can be reciprocated.
A third example of a single-winding linear oscillatory actuator is found in “A linear oscillatory actuator” disclosed in Japanese Laid-open Patent publication No. 113522/1994 (herein after referred to a “third example”).
The linear oscillatory actuator of the third example is configured so that the mover coil is moved by a large force in one direction and returned to an initial position by a small force during a linear reciprocal movement thereof. This device has an actuator body classified as a moving coil type, and a control circuit for controlling so that a large current is supplied to the mover coil in the excitation thereof only when it moves the specified direction. Thus, it is possible to move the mover coil with a high thrust in the specified direction by supplying a large current thereto and to move the mover coil in a reverse direction with a low thrust by supplying a small current to the mover coil.
In the first example, it is possible to realize a single-winding linear oscillatory actuator moving in one direction with a large force and the other direction with a small force by deviating the balance between the magnitude of current and the restoring force of the spring. However, this device is limited since the reciprocal movement is restricted to a specific oscillatory frequency based upon the mechanical characteristics of the spring. In addition, because of the spring, the actuator of the first example is bulky and difficult to miniaturize.
In the second and third examples, it is possible to realize a desired reciprocal movement without using any spring by reversing the direction of the current supplied to the excitation coil. However, the degree of electric current control required in these actuators requires a complicated driving circuit and increases the manufacturing cost. In addition, the second example is designed with the assumption that it is moved with an equal thrust in either direction of reciprocation. This also results in reduced reliability.
What is required, as discovered by the present inventors, is a linear oscillatory actuator capable of minimization and high reliability.